1. Field of the Invention
The present invention relates to an operating method for a refrigerating system and an air-conditioning system which are applicable for buildings and warehouses with refrigeration.
2. Description of the Prior Art
Generally, a refrigerating system and an air-conditioning system employ a refrigerating machine having a smaller capacity than the capacity corresponding to the maximum value of the load of the system for the purpose of reducing instollation and maintenance cost for the system. The refrigerating machine is operated in an operating method as shown in FIGS. 1 to 3. FIG. 1 shows a variation of the load of the system during the period from the start of air-conditioning operation to the end FIGS. 2 and 3 illustrate a variation of an amount of accumulated quantity of heat and a variation of the refrigerating machine's output during the operation of the refrigerating machine. As seen from the graph in FIG. 1, the load Q.sub.L takes place during the period between an air-conditioning start time T1 and the end time T2. And the maximum value of the load far exceeds the maximum value Q.sub.R Max of the refrigerating machine's output Q.sub.R. Therefore, if the refrigerating machine is started at the time T1, the air-conditioning energy is insufficient by the amount corresponding to the sum of the integrating values S1+S3-S2. In order to avoid this difficulty, the air-conditioning start time is set at time T1' which is earlier than the time T1, and the air-conditioning energy is accumulated in a heat storage tank by a predictive amount of the energy, as shown in FIGS. 2 and 3. In this case, if a refrigerating machine the maximum output Q.sub.R Max of which is used, the installation costs for the system may be saved but a large heat storage tank is required. Inversely, if a refrigerating machine having a large capacity is used, the heat storage tank is small but the system cost is expensive. It is a common practice, therefore, that the value of Q.sub.R Max is suitably selected as a compromise between the system cost and the capacity of the heat storage tank. In the operating method shown in FIGS. 1 to 3, the refrigerating machine must always be operated within the time period that the air-conditioning load takes place. Therefore, the refrigerating machine is operated at the maximum output thereof when the air-conditioning load is largest. In the cooling mode of the air-conditioning system, a time period that the air-conditioning load is high is coincident with one that an ambient temperature is high. For this, the refrigerating machine must be operated at the time that the temperature of cooling water of the refrigerating machine is high, that is, must be operated with a low coefficient of performance of the refrigerating machine. Thus, the conventional operating method of the refrigerating machine is disadvantageous in that the operating cost of the air-conditioning system increases.
A Japanese patent publication No. 46501/'72 discloses another type of refrigerating system in which the refrigerating machine is operated at night to accumulate a predetermined amount of heat and, at the same time, an amount of heat to be used on that day is predicted. When the predictive heat amount is larger than the accumulated heat amount, the refrigerating machine is operated by using surplus power in the day time to compensate for the insufficient amount of the heat.